Levoglucosan Yield Research Articles

Acid-catalysed cellulose pyrolysis at low temperatures

This study reports the pyrolysis of the acid-impregnated cellulose at 50–325°C. The presence of acid is found to significantly change cellulose pyrolysis mechanism. While the pyrolysis of raw cellulose mainly proceeds with depolymerisation reactions, the pyrolysis of the acid-impregnated cellulose is dominantly contributed by dehydration reactions. The acid impregnation process seems to weaken the hydrogen bonding networks in cellulose, promoting the formation of glucose oligomers as reaction intermediates. Due to the presence of acid in the reaction intermediates, the glucose oligomers are rapidly hydrolysed to glucose, especially at low temperatures (i.e., 100°C) where the evaporation of produced water (via dehydration) is slow. The results also suggest that glucose is subsequently dehydrated to low molecular weight compounds at increased temperatures. The highly dehydrated cellulose further suppresses the depolymerisation reactions, resulting in a low levoglucosan yield during acid-catalysed pyrolysis of cellulose. The highly dehydrated cellulose also favours char formation likely via furanic structures which are finally transformed into aromatic structures at temperatures >300°C.

Comparison of ethanol production from corn cobs and switchgrass following a pyrolysis-based biorefinery approach.

BackgroundOne of the main obstacles in lignocellulosic ethanol production is the necessity of pretreatment and fractionation of the biomass feedstocks to produce sufficiently pure fermentable carbohydrates. In addition, the by-products (hemicellulose and lignin fraction) are of low value, when compared to dried distillers grains (DDG), the main by-product of corn ethanol. Fast pyrolysis is an alternative thermal conversion technology for processing biomass. It has recently been optimized to produce a stream rich in levoglucosan, a fermentable glucose precursor for biofuel production. Additional product streams might be of value to the petrochemical industry. However, biomass heterogeneity is known to impact the composition of pyrolytic product streams, as a complex mixture of aromatic compounds is recovered with the sugars, interfering with subsequent fermentation. The present study investigates the feasibility of fast pyrolysis to produce fermentable pyrolytic glucose from two abundant lignocellulosic biomass sources in Ontario, switchgrass (potential energy crop) and corn cobs (by-product of corn industry).ResultsDemineralization of biomass removes catalytic centers and increases the levoglucosan yield during pyrolysis. The ash content of biomass was significantly decreased by 82–90% in corn cobs when demineralized with acetic or nitric acid, respectively. In switchgrass, a reduction of only 50% for both acids could be achieved. Conversely, levoglucosan production increased 9- and 14-fold in corn cobs when rinsed with acetic and nitric acid, respectively, and increased 11-fold in switchgrass regardless of the acid used. After pyrolysis, different configurations for upgrading the pyrolytic sugars were assessed and the presence of potentially inhibitory compounds was approximated at each step as double integral of the UV spectrum signal of an HPLC assay. The results showed that water extraction followed by acid hydrolysis and solvent extraction was the best upgrading strategy. Ethanol yields achieved based on initial cellulose fraction were 27.8% in switchgrass and 27.0% in corn cobs.ConclusionsThis study demonstrates that ethanol production from switchgrass and corn cobs is possible following a combined thermochemical and fermentative biorefinery approach, with ethanol yields comparable to results in conventional pretreatments and fermentation processes. The feedstock-independent fermentation ability can easily be assessed with a simple assay.

Effect of acid additives on sugarcane bagasse pyrolysis: Production of high yields of sugars

The aim of this work was to improve sugarcane bagasse thermochemical conversion to pyrolytic sugars production, particularly to levoglucosan. The experiments were carried out evaluating the effect of acid washing with HNO3 (0.1wt.%) followed by H2SO4 addition (0.1, 0.2 and 0.3wt.%) at pyrolysis temperatures of 350, 400, 450, 500, 550 and 600°C was studied by Py-GC/MS. The experimental results showed that HNO3 washing, followed by H2SO4 concentration of 0.2wt.% at 350°C resulted in an increase in levoglucosan yield between 5 and 7 times the yield obtained when the raw bagasse was processed. Thus, these results are very attractive to improve pyrolytic sugars production in sugarcane bagasse by previously acid treatment to pyrolysis technology.

Comparison of Acids and Sulfates for Producing Levoglucosan and Levoglucosenone by Selective Catalytic Fast Pyrolysis of Cellulose Using Py-GC/MS

Levoglucosan (LG) and levoglucosenone (LGO) are two high-valued chemicals, which can be produced by catalytic fast pyrolysis of cellulose with proper catalysts. This work investigated the catalytic characteristics of different acids and metal salt catalysts to produce LG and LGO using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetric analysis (TGA). The results showed that weak acids (such as formic acid and acetic acid) enhanced LG yield, whereas sulfuric acid and phosphoric acid promoted the yield and selectivity of LGO with inhibitory effects on LG production. The maximum LGO selectivity of 61.8% was obtained with 10% phosphoric acid, while the maximum LG selectivity of 87.6% was obtained with 10% acetic acid. In comparison with two impregnation methods, the filtration method can increase LGO yield, while the evaporation method enhanced the selectivity of LGO (up to 82.6%) with lower concentration of phosphoric acid. The effects of metal salts on pyrolysis of cellulose wer...

Effect of pyrolysis conditions on levoglucosan yield from cotton straw and optimization of levoglucosan extraction from bio-oil

Fast pyrolysis of cotton straw was performed under different temperature ranges, particle sizes, holding times and acid concentrations in a fluidized bed reactor to maximize the yield of levoglucosan (LG). The maximum LG yield was obtained at the optimal pyrolytic conditions: temperature of 500°C, holding time of 1.4s, particle size of 600–650μm and acid concentration of 8%. Furthermore, an improved method to quickly and easily extract LG from bio-oil was developed by utilizing precipitation and Soxhlet extraction to quantitatively remove organic colloid, pigments and aromatic compounds with less loss of LG during extraction. The process was optimized by using Box-Behnken design for three reaction parameters: the volume of water (A), the quality of activiaed carbon (B), and pH (C). The extraction presented required no prolonged high heating (thus protecting the LG from hydrolysis), used benign reagents, and realized a significant purity over other methods. The purity and structure of LG were determined by busing chromatographic and spectroscopic techniques, such as HPLC, FT-IR and NMR spectroscopy. The optimal extraction yield of LG from the straw bio-oil was 78% with the purity of 95.56%. This research also applied a new method to quickly determine the quantitative and qualitative analysis test parameters of LG.

The integration of dilute acid hydrolysis of xylan and fast pyrolysis of glucan to obtain fermentable sugars.

BackgroundFermentable sugars are important intermediates in the biological conversion of biomass. Hemicellulose and amorphous cellulose are easily hydrolyzed to fermentable sugars in dilute acid, whereas crystalline cellulose is more difficult to be hydrolyzed. Cellulose fast pyrolysis is an alternative method to liberate valuable fermentable sugars from biomass. The amount of levoglucosan generated from lignocellulose by fast pyrolysis is usually lower than the theoretical yield based on the cellulose fraction. Pretreatment is a promising route to improve the yield of levoglucosan from lignocellulose.ResultsThe integration of dilute sulfuric acid hydrolysis and fast pyrolysis to obtain fermentable sugars was evaluated in this study. Dilute sulfuric acid hydrolysis could remove more than 95.1 and 93.4 % of xylan (the main component of hemicellulose) from sugarcane bagasse and corncob with high yield of xylose. On the other hand, dilute sulfuric acid hydrolysis was also an effective pretreatment to enhance levoglucosan yield from lignocellulose. Dilute acid hydrolysis could accumulate glucan (the component of cellulose) and remove most of the alkali and alkaline earth metals which were powerful catalysts during fast pyrolysis. Further increase in dilute acid concentration (from 0 to 2 %) in pretreatment could promote the yield of levoglucosan in fast pyrolysis. The acid pretreated sugarcane bagasse and corncob gave levoglucosan yields of 43.8 and 35.2 % which were obvious higher than those of raw sugarcane bagasse (12.0 %) and corncob (7.0 %).ConclusionsObtaining fermentable sugars by combination dilute acid hydrolysis of xylan and fast pyrolysis of glucan could make full utilization of biomass, and get fermentable sugars economically from biomass for bio-refinery.

Effect of KCl and CaCl2 loading on the formation of reaction intermediates during cellulose fast pyrolysis

The influence of KCl and CaCl2 on the primary reactions of cellulose pyrolysis is studied using a wire-mesh reactor from 250°C to 600°C, focusing on the reaction intermediates. A pre- column derivatization with benzoyl chloride prior to HPLC analysis is applied for the quantification of anhydro-sugars (levoglucosan, cellobiosan, maltosan) from pyrolysis. At low temperatures, the additions of inorganics salts, especially CaCl2, weakens hydrogen bonds, resulting in high yields of levoglucosan and cellobiosan from the cleavage of glycosidic bonds rather than from dehydration reactions. At elevated temperatures, dehydration reactions in the sugar units are mainly responsible for the destruction of sugar rings followed by the scission of pyran rings, leading to the weight-loss of CaCl2-loaded cellulose in the form of low molecular weight organic species. Meanwhile, accumulated unsaturated structures suppress the cleavage of glycosidic bonds, leading to the formation of char. However, KCl appears to catalyze the cleavage of glycosidic bonds or the scission of pyran rings directly, which perhaps occurs through a homolytic mechanism, leading to low molecular weight species. Furthermore, maltosan is shown to be a secondary product and is catalyzed by KCl and CaCl2 indirectly through the repolymerization of levoglucosan in the solid phase. A modified mechanism is also proposed regarding cellulose pyrolysis and the primary catalysis of KCl and CaCl2.

Pretreating biomass via demineralisation and torrefaction to improve the quality of crude pyrolysis oil

Pretreating biomass prior to pyrolysis was investigated. Three undesirable catalysts naturally present in biomass were identified: inorganics, acids, and water. A pretreatment sequence incorporating acid leaching and torrefaction was developed to reduce/remove these catalysts. Acid leaching targeted reducing the biomass's inorganic content. The acidic liquor produced during torrefaction was rich in acetic and formic acid; this solution was recycled as the acid leaching reagent. The optimal leaching conditions were at 30 °C with 1% acetic acid for 4 h, which decreased the inorganic content from 0.41 wt% to 0.16 wt% for leached biomass. Torrefaction targeted reducing the biomass's moisture and acetyl content and was optimal at 270 °C for 20 min. Bio-oil from pyrolysis of demineralisation and torrefied biomass was depleted in organic acids, pyrolytic lignin, and water but was rich in levoglucosan and aromatics. Decreasing the biomass's acetyl and inorganic content reduced organic acid formation. The water content in the bio-oil was lower because less water entered the system, and water plays an auto-catalytic role during pyrolysis, promoting the production of pyrolytic water. The high levoglucosan yield confirmed that secondary reactions were limited to a much higher degree when both pretreatments were implemented compared to demineralisation or torrefaction alone.

Influence mechanism of torrefaction on softwood pyrolysis based on structural analysis and kinetic modeling

The influence mechanism of torrefaction on biomass pyrolysis was studied in detail. 13C CP/MAS NMR was employed to characterize the evolution of functional groups during torrefaction, indicating that hemicellulose was extensively deacetylated and depolymerized; the crystalline structure of cellulose was destroyed; and the aryl ether linkages and propyl side branches in lignin were cleaved. A distributed activation energy model with three combined Gaussian functions was introduced to analyze the pyrolysis kinetics of biomass. The mean activation energies for three parallel reactions remained unchanged after torrefaction, while the weighing factors proved that their contributions to devolatilization largely changed. Acetic acid yield significantly decreased after torrefaction, with reduction of the yields of 5-hydroxymethylfurfural and levoglucosan because of the depolymerization of carbohydrates during torrefaction. Due to the dissociation of propyl branches and the demethylation of methoxyls in lignin, pyrolysis of torrefied biomass yielded more guaiacol and catechol and less phenols with C4-propyl groups.

Fast pyrolysis of glucose‐based carbohydrates with added NaCl part 2: Validation and evaluation of the mechanistic model

A mechanistic model considering the significant catalytic effects of Na+ on fast pyrolysis of glucose‐based carbohydrates was developed in Part 1 of this study. A computational framework based on continuous distribution kinetics and mass action kinetics was constructed to solve the mechanistic model. Agreement between model yields of various pyrolysis products with experimental data from fast pyrolysis of glucose‐based carbohydrates dosed with NaCl ranging from 0–0.34 mmol/g at 500 °C validated the model and demonstrated the robustness and extendibility of the mechanistic model. The model was able to capture the yields of major and minor products as well as their trends across NaCl concentrations. Modeling results showed that Na+ accelerated the rate of decomposition and reduced the time for complete thermoconversion of carbohydrates. The sharp reduction in the yield of levoglucosan (LVG) from fast pyrolysis of cellulose in the presence of NaCl was mainly caused by reduced decomposition of cellulose chains via end‐chain initiation and depropagation due to Na+ favoring competing dehydration reactions. Analysis of the contributions of reaction pathways showed that the decomposition of LVG made a minor contribution to its yield reduction and contributed less than 0.5% to the final yield of glycolaldehyde from fast pyrolysis of glucose‐based carbohydrates in the presence of NaCl. © 2015 American Institute of Chemical Engineers AIChE J, 62: 778–791, 2016

Lignocellulose pyrolysis with condensable volatiles quantification by thermogravimetric analysis—Thermal desorption/gas chromatography–mass spectrometry method

A thermogravimetric analysis technique coupled to an evolved gas analysis, namely the thermal desorption/gas chromatography–mass spectrometry method (TGA–TD/GC-MS) was developed, to identify and quantify condensable volatile compounds produced during the pyrolysis of lignocellulose. Four lignocellulose samples of different origins (i.e., pine, bamboo, corn cob and corn stover) were pyrolysed using a TGA system. Condensable volatiles released during pyrolysis were captured onto thermal desorption tubes and subsequently identified and quantified using a TD/GC–MS method. Chemical composition of condensable volatiles was statistically correlated with the original lignocellulose composition, using Principal Component Analysis (PCA). A total of 15–19wt% (dry weight) of biomass pyrolysis products were quantified by the method, with an average Relative Standard Deviation on the high concentration condensable volatiles yield of 6.4%, a significant improvement to what has been reported in literature. The first two principal components accounted for 89.4% of the variance in the data and showed clear correlations between evolved condensable volatile compounds and compositional differences among the four biomass samples. The origin of most lignin-derived compounds could be determined, due to the limitation of secondary reactions under slow pyrolysis. The yield of levoglucosan and 5-hydroxymethylfurfural were consistent with the initial content of C6 sugars in the feedstock, but also negatively correlated with the ash content. The quantification of acetic acid, the highest yielding condensable volatile product, can be used as an indicator of the number of acetyl groups in biomass.

The comparison of obtaining fermentable sugars from cellulose by enzymatic hydrolysis and fast pyrolysis

Sugars are one of intermediates in the biological and chemical conversion of biomass. The objective of this study was to make comparison of obtaining fermentable sugars by enzymatic hydrolysis and fast pyrolysis of ball milling pretreated cellulose. After ball milling pretreatment for 0–18h, with the accumulation of alkali and alkali earth metals (from 50.8 to 276.4ppm) and decrease of the crystalline structure (from 89.8% to 10.1%), the hydrolysis yields increased from 23.6% to 56.0% in enzymatic saccharification, while the yields of levoglucosan diminished from 61.5% to 45.6% gradually in fast pyrolysis. Both enzymatic saccharification and fast pyrolysis had unique attractive features and unfavorable limitations. The present research provided a concept for considering choices among the technologies and feedstocks currently available.

Value added liquid products from waste biomass pyrolysis using pretreatments

Douglas fir wood, a forestry waste, was attempted to be converted into value added products by pretreatments followed by pyrolysis. Four different types of pretreatments were employed, namely, hot water treatment, torrefaction, sulphuric acid and ammonium phosphate doping. Subsequently, pyrolysis was done at 500°C and the resulting bio-oils were analysed for their chemical composition using Karl Fischer titration, thermogravimetry, ion exchange, and gas chromatography. Pretreatment with acid resulted in the highest yield of bio-oil (~60%). The acid and salt pretreatments were responsible for drastic reduction in the lignin oligomers and enhancement of water content in the pyrolytic liquid. The quantity of xylose/mannose reduced as a result of pretreatments. Although, the content of fermentable sugars remained similar across all the pretreatments, the yield of levoglucosan increased. Pretreatment of the biomass with acid yielded the highest amount of levoglucosan in the bio-oil (13.21%). The acid and salt pretreatments also elevated the amount of acetic acid in the bio-oils. Addition of acid and salt to the biomass altered the interaction of cellulose–lignin in the pyrolysis regime. Application of pretreatments should be based on the intended end use of the liquid product having a desired chemical composition.

Comprehensive utilization of glycerol from sugarcane bagasse pretreatment to fermentation

In this study, the effects of glycerol pretreatment on subsequent glycerol fermentation and biomass fast pyrolysis were investigated. The liquid fraction from the pretreatment process was evaluated to be feasible for fermentation by Paenibacillus polymyxa and could be an economic substrate. The pretreated biomass was further utilized to obtain levoglucosan by fast pyrolysis. The pretreated sugarcane bagasse exhibited significantly higher levoglucosan yield (47.70%) than that of un-pretreated sample (11.25%). The promotion could likely be attributed to the effective removal of alkali and alkaline earth metals by glycerol pretreatment. This research developed an economically viable manufacturing paradigm to utilize glycerol comprehensively and enhance the formation of levoglucosan effectively from lignocellulose.

Cellulose-Lignin interactions during slow and fast pyrolysis

The interactions between lignin and cellulose during the slow pyrolysis of their blends were studied by means of Thermogravimetric Analysis (TGA) and Scanning Electron Microscopy (SEM). Fast pyrolysis was studied using Pyrolysis-Gas Chromatography/Mass Spectroscopy (Py–GC/MS). Crystalline cellulose (Avicel), amorphous cellulose, organosolv lignin, and their blends containing 20, 50, and 80wt.% of lignin were used for the experiments. Differential thermogravimetry (DTG) revealed that the interaction between crystalline cellulose and lignin resulted in a shift toward higher decomposition temperatures, but for lignin/amorphous cellulose mixtures this effect was small. No effect of adding lignin to cellulose was observed on the yields of bio-char. Cellulose-lignin interactions during fast pyrolysis in Py–GC/MS did occur. Products from cellulose fragmentation reactions (hydroxyl-acetaldehyde and acetol) were not influenced by the presence of lignin. In general, production of lignin derived phenolics remains quite similar at 500°C, but the yield of many methoxylated monophenols increases at 350°C in the presence of both types of cellulose. Importantly, it was found that the presence of lignin enhanced the yield of levoglucosan, but decreased the yield of some of their dehydration products (e.g., levoglucosenone, 5-Hydrosymethylfurfural, Furfural). This result could be explained by the reduction of residence time of cellulose products in liquid intermediates, a phase where most of the dehydration reactions occur. Lignin seems to enhance micro-explosions, decreasing in this way the residence time of cellulose derived products in the liquid intermediates.

Impact of combined acid washing and acid impregnation on the pyrolysis of Douglas fir wood

This study reports the impact of acid washing (to remove alkali and alkaline earth metals) followed by mild acid impregnation on the pyrolysis of Douglas fir wood. Dilute nitric acid was used in the washing and sulfuric acid, acetic acid, nitric acid, and phosphoric acid at acid loading levels of 0.05, 0.1, 0.3, and 0.5wt.% were used for the acid impregnation to improve the yield of levoglucosan. A Py–GC/MS instrument was used to semi-quantitatively measure the impact of various acids and concentrations on the yield of low molecular weight compounds released during pyrolysis at 500°C. The nitric acid wash removed 56% of the metal content. The results confirmed all the acids studied increased the production of levoglucosan, likely due to the mitigation of undesirable interactions between the cellulose and the other constituents of the lignocellulosic matrix. The highest yields of levoglucosan were achieved with the strong acids: sulfuric acid loading of 0.05wt.%, nitric acid 0.05wt.% and phosphoric acid 0.3wt.%. Sulfuric and phosphoric acid also enhanced dehydration reactions in cellulose products and decreased the production of methoxylated phenolics from lignin. The very small range of concentration at which these acids increase levoglucosan yield makes it very difficult to control the process. In the case of acetic acid, it is not strong enough to catalyze dehydration reactions. Consequently a much wider range of concentrations can be used thus facilitating the control of the process. Acetic acid also does not affect the yield of lignin products. Therefore, acetic acid appears to be the most practical for acid impregnation (following mineral removal) in wood pyrolysis.

Microwave Pyrolysis of Biomass: Control of Process Parameters for High Pyrolysis Oil Yields and Enhanced Oil Quality

The oil yield and quality of pyrolysis oil from microwave heating of biomass was established by studying the behavior of Larch in microwave processing. This is the first study in biomass pyrolysis to use a microwave processing technique and methodology that is fundamentally scalable, from which the basis of design for a continuous processing system can be derived to maximize oil yield and quality. It is shown systematically that sample size is a vital parameter that has been overlooked by previous work in this field. When sample size is controlled, the liquid product yield is comparable to conventional pyrolysis and can be achieved at an energy input of around 600 kWh/t. The quality of the liquid product is significantly improved compared to conventional pyrolysis processes, which results from the very rapid heating and quenching that can be achieved with microwave processing. The yields of levoglucosan and phenolic compounds were found to be an order of magnitude higher in microwave pyrolysis when compared with conventional fast pyrolysis. Geometry is a key consideration for the development of a process at scale, and the opportunities and challenges for scale-up are discussed within this paper.

Obtaining fermentable sugars by dilute acid hydrolysis of hemicellulose and fast pyrolysis of cellulose

The objective of this study was to get fermentable sugars by dilute acid hydrolysis of hemicellulose and fast pyrolysis of cellulose from sugarcane bagasse. Hemicellulose could be easily hydrolyzed by dilute acid as sugars. The remained solid residue of acid hydrolysis was utilized to get levoglucosan by fast pyrolysis economically. Levoglucosan yield from crystalline cellulose could be as high as 61.47%. Dilute acid hydrolysis was also a promising pretreatment for levoglucosan production from lignocellulose. The dilute acid pretreated sugarcane bagasse resulted in higher levoglucosan yield (40.50%) in fast pyrolysis by micropyrolyzer, which was more effective than water washed (29.10%) and un-pretreated (12.84%). It was mainly ascribed to the effective removal of alkali and alkaline earth metals and the accumulation of crystalline cellulose. This strategy seems a promising route to achieve inexpensive fermentable sugars from lignocellulose for biorefinery.

Influence of possible interactions between biomass organic components and alkali metal ions on steam assisted pyrolysis: A case study on Arundodonax

The influence of feedstock composition (organic and inorganic matrix) on the products yields and the liquid phase composition deriving from a slow steam assisted pyrolysis process was studied. To this aim, slow steam assisted pyrolysis tests at 5K/min and final temperature equal to 973K were carried out on cellulose (pure and doped with Na and K ions), on a biomass model mixture of cellulose, xylan and lignin alkali and on Arundo donax canes, untreated and demineralized. Products yields were measured. Chromatographic techniques were applied to identify and quantify the main species in the gaseous and in the liquid fractions. This study showed that alkali metal ions affected both the devolatilization and gasification stages. More specifically, their presence depressed the levoglucosan yield due to cellulose decomposition and enhanced the production of CO2 and H2 in the gasification stage.

Cellulose–Hemicellulose and Cellulose–Lignin Interactions during Fast Pyrolysis

Previously, the primary product distribution resulting from fast pyrolysis of cellulose, hemicellulose, and lignin was quantified. This study extends the analysis to the examinations of interactions between cellulose–hemicellulose and cellulose–lignin, which were determined by comparing the pyrolysis products from their native mixture, physical mixture, and superposition of individual components. Negligible interactions were found for both binary physical mixtures. For the native cellulose–hemicellulose mixture, no significant interaction was identified either. In the case of the native cellulose–lignin mixture, herbaceous biomass exhibited an apparent interaction, represented by diminished yield of levoglucosan and enhanced yield of low molecular weight compounds and furans. However, such an interaction was not found for woody biomass. It is speculated that these results are due to different amounts of covalent linkages in these biomass samples. This study provides insight into the chemistry involved during the pyrolysis of multicomponent biomass, which can facilitate building a model for bio-oil composition prediction.